Utility of the Kidney Failure Risk Equation and Estimated GFR for Estimating Time to Kidney Failure in Advanced CKD

Abstract

Rationale & objective: The Kidney Failure Risk Equation (KFRE) predicts the 2-year risk of kidney failure for patients with chronic kidney disease (CKD). Translating KFRE-predicted risk or estimated glomerular filtration rate (eGFR) into time to kidney failure could inform decision making for patients approaching kidney failure.

Study design: Retrospective cohort.

Setting & participants: CKD Outcomes and Practice Patterns Study (CKDOPPS) cohort of patients with an eGFR<60mL/min/1.73m² from 34 US nephrology practices (2013-2021).

Exposure: 2-year KFRE risk or eGFR.

Outcome: Kidney failure defined as initiation of dialysis or kidney transplantation.

Analytical approach: Accelerated failure time (Weibull) models used to estimate the median, 25th, and 75th percentile times to kidney failure starting from KFRE values of 20%, 40%, and 50%, and from eGFR values of 20, 15, and 10mL/min/1.73m². We examined variability in time to kidney failure by age, sex, race, diabetes status, albuminuria, and blood pressure.

Results: Overall, 1,641 participants were included (mean age 69±13 years; median eGFR of 28mL/min/1.73m² [IQR 20-37mL/min/1.73 m²]). Over a median follow-up period of 19 months (IQR, 12-30 months), 268 participants developed kidney failure, and 180 died before reaching kidney failure. The median estimated time to kidney failure was widely variable across patient characteristics from an eGFR of 20mL/min/1.73m² and was shorter for younger age, male sex, Black (versus non-Black), diabetes (vs no diabetes), higher albuminuria, and higher blood pressure. Estimated times to kidney failure were comparably less variable across these characteristics for KFRE thresholds and eGFR of 15 or 10mL/min/1.73m².

Limitations: Inability to account for competing risks when estimating time to kidney failure.

Conclusions: Among those with eGFR<15mL/min/1.73m² or KFRE risk>40%), both KFRE risk and eGFR showed similar relationships with time to kidney failure. Our results demonstrate that estimating time to kidney failure in advanced CKD can inform clinical decisions and patient counseling on prognosis, regardless of whether estimates are based on eGFR or the KFRE.

Plain-language summary: Clinicians often talk to patients with advanced chronic kidney disease about the level of kidney function expressed as the estimated glomerular filtration rate (eGFR) and about the risk of developing kidney failure, which can be estimated using the Kidney Failure Risk Equation (KFRE). In a cohort of patients with advanced chronic kidney disease, we examined how eGFR and KFRE risk predictions corresponded to the time patients had until reaching kidney failure. Among those with eGFR<15mL/min/1.73m² or KFRE risk > 40%), both KFRE risk and eGFR showed similar relationships with time to kidney failure. Estimating time to kidney failure in advanced CKD using either eGFR or KFRE can inform clinical decisions and patient counseling on prognosis.

Keywords: Chronic kidney disease; KFRE; end-stage kidney disease; kidney failure; kidney failure risk equation.

Figure 1.. Study flow diagram

Abbreviations: CKDopps = CKD Outcomes and Practice Patterns Study; KFRE = Kidney Failure Risk Equation.

Figure 2.. Calibration of 2-Year Kidney Failure Risk Equation

Points represent deciles of predicted risk. The diagonal line indicates perfect calibration. Observed risk was computed as the 2-year cumulative incidence of kidney failure.

Figure 3.. Estimated median (IQR) time to kidney failure by KFRE or eGFR

The solid line indicates median estimated time to kidney failure. The dotted lines indicate 25^th and 75^th percentile times to kidney failure. Histograms show the number of observations in the analytic cohort over the range of KFRE or eGFR values. Abbreviations: eGFR = estimated glomerular filtration rate; IQR = interquartile range; KFRE = Kidney Failure Risk Equation.

Figure 4.. Estimated median (IQR) time to kidney failure from eGFR or 2-year KFRE threshold values by participant characteristic

Asterisks indicate statistically significant differences to a level of p <0.05 between estimated median time to kidney failure. Dashed lines and arrowheads indicate estimates for median or IQR extending beyond the maximum observed follow up time. Abbreviations: DM = diabetes mellitus; eGFR = estimated glomerular filtration rate; IQR = interquartile range; KFRE = Kidney Failure Risk Equation; SBP = systolic blood pressure; UACR = urine albumin/creatinine ratio.